In the hot water extraction method, hot water is essentially sprayed on the carpet and then sucked back into the machine, along with any dirt that was in the carpet. There is usually a cleaning solution added into the water to assist in the removal of stains.
The primary method of carpet cleaning recommended by carpet manufacturers is hot water extraction — more commonly (though slightly imprecisely) known as steam cleaning.
Technically speaking, true steam cleaning does not spray water on the carpet, but rather heats the water and uses the resulting steam to clean the fibers. However, today it is widely accepted that the term steam cleaning actually refers to hot water extraction, the most common cleaning process.